This invention relates to plastic hinges and more particularly to an integral hinge formed in a molded plastic container.
Historically plastic articles such as Expandable Polystyrene beads have been molded into cartons and boxes for containing merchandise and the like for a wide variety of packaging applications. Initially, the top was made as a separate piece from the bottom and was held on with a tie or plastic tape when it was desired to close the container. Another common use of this type of packaging was to place the Expandable Polystyrene container top and bottom, in a cardboard sleeve that would hold them together. Gradually attempts have been made to form a hinge in the plastic by compressing the plastic into a narrow longitudinal trough along one edge joining a top and bottom, which can be readily bent to permit the closure of the top onto the bottom.
"Living" hinges of various types have been available in plastics such as polypropylene and polyethylene wherein by heat and pressure a linear indentation is made that permits the bending of the plastic sheet along this thinned and formed section of the basic plastic sheet. For foamed plastic containers such as those made from Expandable Polystyrene where the density of the plastic is substantially less, it has been found, a hinge of this type has insufficient structural tensil and bending strength. Heretofore a "hinged" Expandable Polystyrene container could only be bent a very few times before breaking completely apart.